Automobiles have been equipped with bumper beams since the early decades of their development, as crash-resistant structural parts that are mounted to the front of the automobiles in order to withstand impact force in the event of a crash to prevent or limit internal damage to the automobiles. Nowadays, most jurisdictions require bumper beams on both front and rear of the automobiles, while similar crash-resistant structural parts may additionally be provided, e.g., at sidewalls or across the top of the automobiles.
In currently manufactured automobiles, the bumper beams are usually hidden from view underneath a cover conforming to an automobile body design and are typically made of steel, being assembled with additional parts such as crash boxes for absorbing impact energy. While steel has the necessary strength and stiffness required for crash resistance, it is also heavy and difficult to have complex shapes demanded by the automobile body design. Therefore, it is often necessary to construct a bumper beam assembly including further elements, such as additional stiffeners and brackets linking the stiffeners to the bumper beam, which further adds weight and complicates manufacturing.
U.S. Pat. No. 6,346,325 B1 discloses manufacturing a bumper beam as a fiber-reinforced rigid thermoplastic composite article by making use of a depolymerization-repolymerization (DPRP) mechanism. The manufacturing process includes drawing a fiber bundle continuously through a melt obtained by heating rigid thermoplastic polyurethane that contains a catalyst to a temperature sufficient to depolymerize the thermoplastic polyurethane. The drawn fiber bundle is impregnated with the depolymerized thermoplastic polyurethane to form a composite melt. The composite melt is shaped into an article, and the article is encased with a thermoplastic resin.
However, because there is a maximum temperature to which the melt can be heated without losing its ability to repolymerize, the viscosity of the melt during impregnation of the fiber bundle is limited by a corresponding minimum viscosity, which poses an upper limit on the fiber content, and therefore, the strength-to-weight ratio achievable in the finished article. Accordingly, it is desirable to provide a bumper beam or other crash-resistant structural part for an automobile that has a favorable strength-to-weight ratio and is easy to manufacture.